Drop unnecessary srcdir paths

There's no need to specify the srcdir explicitly in _HEADERS and
EXTRA_DIST.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10493

include/os/linux/spl/rpc/Makefile.am

@@ -1,5 +1,5 @@
 KERNEL_H = \
-	$(top_srcdir)/include/os/linux/spl/rpc/xdr.h
+	xdr.h
 
 if CONFIG_KERNEL
 kerneldir = @prefix@/src/zfs-$(VERSION)/include/spl/rpc

include/os/linux/spl/sys/Makefile.am

@@ -1,62 +1,62 @@
 KERNEL_H = \
-	$(top_srcdir)/include/os/linux/spl/sys/acl.h \
-	$(top_srcdir)/include/os/linux/spl/sys/atomic.h \
-	$(top_srcdir)/include/os/linux/spl/sys/byteorder.h \
-	$(top_srcdir)/include/os/linux/spl/sys/callb.h \
-	$(top_srcdir)/include/os/linux/spl/sys/callo.h \
-	$(top_srcdir)/include/os/linux/spl/sys/cmn_err.h \
-	$(top_srcdir)/include/os/linux/spl/sys/condvar.h \
-	$(top_srcdir)/include/os/linux/spl/sys/console.h \
-	$(top_srcdir)/include/os/linux/spl/sys/cred.h \
-	$(top_srcdir)/include/os/linux/spl/sys/ctype.h \
-	$(top_srcdir)/include/os/linux/spl/sys/debug.h \
-	$(top_srcdir)/include/os/linux/spl/sys/disp.h \
-	$(top_srcdir)/include/os/linux/spl/sys/dkio.h \
-	$(top_srcdir)/include/os/linux/spl/sys/errno.h \
-	$(top_srcdir)/include/os/linux/spl/sys/fcntl.h \
-	$(top_srcdir)/include/os/linux/spl/sys/file.h \
-	$(top_srcdir)/include/os/linux/spl/sys/inttypes.h \
-	$(top_srcdir)/include/os/linux/spl/sys/isa_defs.h \
-	$(top_srcdir)/include/os/linux/spl/sys/kmem_cache.h \
-	$(top_srcdir)/include/os/linux/spl/sys/kmem.h \
-	$(top_srcdir)/include/os/linux/spl/sys/kstat.h \
-	$(top_srcdir)/include/os/linux/spl/sys/list.h \
-	$(top_srcdir)/include/os/linux/spl/sys/mod_os.h \
-	$(top_srcdir)/include/os/linux/spl/sys/mutex.h \
-	$(top_srcdir)/include/os/linux/spl/sys/param.h \
-	$(top_srcdir)/include/os/linux/spl/sys/processor.h \
-	$(top_srcdir)/include/os/linux/spl/sys/proc.h \
-	$(top_srcdir)/include/os/linux/spl/sys/procfs_list.h \
-	$(top_srcdir)/include/os/linux/spl/sys/random.h \
-	$(top_srcdir)/include/os/linux/spl/sys/rwlock.h \
-	$(top_srcdir)/include/os/linux/spl/sys/shrinker.h \
-	$(top_srcdir)/include/os/linux/spl/sys/sid.h \
-	$(top_srcdir)/include/os/linux/spl/sys/signal.h \
-	$(top_srcdir)/include/os/linux/spl/sys/simd.h \
-	$(top_srcdir)/include/os/linux/spl/sys/stat.h \
-	$(top_srcdir)/include/os/linux/spl/sys/strings.h \
-	$(top_srcdir)/include/os/linux/spl/sys/sunddi.h \
-	$(top_srcdir)/include/os/linux/spl/sys/sysmacros.h \
-	$(top_srcdir)/include/os/linux/spl/sys/systeminfo.h \
-	$(top_srcdir)/include/os/linux/spl/sys/taskq.h \
-	$(top_srcdir)/include/os/linux/spl/sys/thread.h \
-	$(top_srcdir)/include/os/linux/spl/sys/time.h \
-	$(top_srcdir)/include/os/linux/spl/sys/timer.h \
-	$(top_srcdir)/include/os/linux/spl/sys/trace.h \
-	$(top_srcdir)/include/os/linux/spl/sys/trace_spl.h \
-	$(top_srcdir)/include/os/linux/spl/sys/trace_taskq.h \
-	$(top_srcdir)/include/os/linux/spl/sys/tsd.h \
-	$(top_srcdir)/include/os/linux/spl/sys/types32.h \
-	$(top_srcdir)/include/os/linux/spl/sys/types.h \
-	$(top_srcdir)/include/os/linux/spl/sys/uio.h \
-	$(top_srcdir)/include/os/linux/spl/sys/user.h \
-	$(top_srcdir)/include/os/linux/spl/sys/vfs.h \
-	$(top_srcdir)/include/os/linux/spl/sys/vmem.h \
-	$(top_srcdir)/include/os/linux/spl/sys/vmsystm.h \
-	$(top_srcdir)/include/os/linux/spl/sys/vnode.h \
-	$(top_srcdir)/include/os/linux/spl/sys/wait.h \
-	$(top_srcdir)/include/os/linux/spl/sys/zmod.h \
-	$(top_srcdir)/include/os/linux/spl/sys/zone.h
+	acl.h \
+	atomic.h \
+	byteorder.h \
+	callb.h \
+	callo.h \
+	cmn_err.h \
+	condvar.h \
+	console.h \
+	cred.h \
+	ctype.h \
+	debug.h \
+	disp.h \
+	dkio.h \
+	errno.h \
+	fcntl.h \
+	file.h \
+	inttypes.h \
+	isa_defs.h \
+	kmem_cache.h \
+	kmem.h \
+	kstat.h \
+	list.h \
+	mod_os.h \
+	mutex.h \
+	param.h \
+	processor.h \
+	proc.h \
+	procfs_list.h \
+	random.h \
+	rwlock.h \
+	shrinker.h \
+	sid.h \
+	signal.h \
+	simd.h \
+	stat.h \
+	strings.h \
+	sunddi.h \
+	sysmacros.h \
+	systeminfo.h \
+	taskq.h \
+	thread.h \
+	time.h \
+	timer.h \
+	trace.h \
+	trace_spl.h \
+	trace_taskq.h \
+	tsd.h \
+	types32.h \
+	types.h \
+	uio.h \
+	user.h \
+	vfs.h \
+	vmem.h \
+	vmsystm.h \
+	vnode.h \
+	wait.h \
+	zmod.h \
+	zone.h
 
 if CONFIG_KERNEL
 kerneldir = @prefix@/src/zfs-$(VERSION)/include/spl/sys